I'm still having a problem in my  Seconds to Period routine for a
Dallas 1994 iButton. So much so I can't even get Maxim's sample code
to work properly (in theory).

I am wondering if there is a maths wiz out there who may be able to
point me in the right direction - I've googled and none of the
results have helped much in fact they've confused me.

The Dallas suggested code for a PC is

void SecondsToDate(timedate *td, ulong x)
{
   short tmp,i,j;
   ulong y;

   // check to make sure date is not over 2070 (sanity check)
   if (x > 0xBBF81E00L)
      x = 0;

   y = x/60;  td->second = (ushort)(x-60*y);
   x = y/60;  td->minute = (ushort)(y-60*x);
   y = x/24;  td->hour   = (ushort)(x-24*y);
   x = 4*(y+731);  td->year = (ushort)(x/1461);
   i = (int)((x-1461*(ulong)(td->year))/4);  td->month = 13;

   do
   {
      td->month -= 1;
      tmp = (td->month > 2) && ((td->year & 3)==0) ? 1 : 0;
      j = dm[td->month]+tmp;

   } while (i < j);

   td->day = i-j+1;

   // slight adjustment to algorithm
   if (td->day == 0)
      td->day = 1;

   td->year = (td->year < 32)  ? td->year + 68 + 1900: td->year - 32
+ 2000;
}


Now with this if I work through for the date 31/12/ 2003  @ 23:59:59
I end up with a year 11 before I get to the 200 adjustment.

This is my code after taking year 2000 as the base year. It works
apart from the above date where it rolls over to the 32/1/2003 and
waits 24 hours before getting to 1st January 2004. Similar problem at
end of leap years January starts on the 2nd but the year and month
roll over correctly.

void secs2period(timecals *pTimeDisp,ulong idata)
{
                ulong temp;
                ulong m;
                ulong d;

                //Max year 31  December 2030 23:59:59,
                if (idata> 0x3A468DFF)
                        idata=0;

                temp=idata/60;
                pTimeDisp->scnd=(idata-60*temp);

                idata=temp/60;
                pTimeDisp->min=(temp-60*idata);

                temp=idata/24;
                pTimeDisp->hr=(idata-24*temp);

                idata=4*(temp+731);
                pTimeDisp->yr=(idata/1461)-2;   //1461= 365.25 days * 4years
                m=temp-(pTimeDisp->yr*365);

                pTimeDisp->mnth=13;

                do
                {
                        pTimeDisp->mnth-=1;
                        temp=(pTimeDisp->mnth > 2) && ((pTimeDisp->yr & 3)==0) ? 1: 0;
                        d=daysofar[timedisp->mnth]+temp;

                }
                while (d>m);

                pTimeDisp->dy=m-d+1;

                if (pTimeDisp->dy==0)
                        pTimeDisp->dy=1;

}

I realise that I need to compensate for fractions of a year, I just
can't see where. My 'C" compiler for the Pic doesn't allow the
casting of structures as written in  the Maxim code, and as it's the
algorithm that's failing me re-writing it in assembler probably won't
get me any further at the moment..

Any help that stops me head banging the wall would be gratefully
received.

Colin

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--
cdb, cdb@barnard.name on 31/03/2002

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